CSc 360 Operating Systems Overview

CSc 360Operating SystemsOverviewJianping PanFall 20079/7/07 CSc 360 1

Review (from the last lecture)• Computer organization and architecture– CPU– Memory– I/O: polling, interrupt, DMA• Operating system– The software that manages CPU, memoryand I/O, as many more9/7/07 CSc 360 2

OS: historical view• Requirements evolve• Was– computers were more expensive than users– goals: make computers more efficiently used– results: share computers• Now– users become more “expensive” than computers– goals: make computers more effectively used– results: share users (among many computers)9/7/07 CSc 360 3

OS: generations• Uniprogramming– “One program at a time”• start, execute, {wait, execute}*, finish• wait for: input/output, other programs, etc• CPU may be idle most of the time• Multiprogramming– “Many programs at a time”• try to keep CPU always busy• handle multiple programs at the same time• “share” (a) CPU9/7/07 CSc 360 4

Batch processing• Load a pool of jobs• Execute one job until it is blocked• Pick another one to execute9/7/07 CSc 360 5

Time sharing• Execute one job up to a certain time– e.g., hardware timer with counter• Switch to another one to execute– job scheduling, memory swapping• Seem to execute many jobs at the same time• Batch processing vs time sharing– job responsiveness– switching overhead9/7/07 CSc 360 6

• Interrupt the current job– yield: system call trap (e.g., I/O)– yank: hardware timer interrupt– how about an “abusive” job?• Dual-mode operation– user mode for regular applications– kernel mode with privileged instructions– trap: user to kernel entryOS:operations9/7/07 CSc 360 7

Process management• Process: a running program– vs thread• Create, delete, suspend, resume process– resource allocation: CPU, memory, I/O, etc• Schedule processes/threads• Synchronize processes• Communicate between processes• Handle deadlocks9/7/07 CSc 360 8

Memory management• (Main) memory– store instructions for execution– store data for processing• Keep track available memory• Allocate and reclaim memory– provide protected access– trap invalid access• Swap in/out (virtual) memory9/7/07 CSc 360 9

Storage and I/O management• “In Unix, everything is a file”– a logical interface: open, read, write• Create and delete files and directories– directory is a special file– file system hierarchy• Manipulate files and directories– provide protected access– handle device-specific issues (disks, etc)9/7/07 CSc 360 10

User management• Authentication– who's who– user credentials (e.g., password, token)• Authorization– what can do what– access control (e.g., read, write, execute)• Accounting– what has been done (e.g., logging)9/7/07 CSc 360 11

Specialized OS• Different requirements and constraints– real-time systems• “hard” real-time OS in embedded systems• “soft” real-time OS in multimedia systems– handheld systems• almost a full-blown OS, with resourceconstraints– embedded systems• very severe resource constraints9/7/07 CSc 360 12

This lecture• An overview on operating systems– Multiprogramming• Batch processing vs time sharing– Dual-mode operations– Issues in• process management• memory management• file management9/7/07 CSc 360 13

Next lecture• Interfaces to OS– CLI, GUI, system calls, API– read OSC7 Chapter 2 (or OSC6 Chapter 3)9/7/07 CSc 360 14